It looks as though this page is just a placeholder and this device has not actually
been released yet (I don't see it on Amazon or Ebay, their usual avenues for selling)
I don't know if I'll be getting one, given the rather steep cost of the Wii U Pro controllers.
But still, the idea is pretty cool. They've also got a similar adapter for PS3 controllers.

I already have their wireless adapter for the original flatties (and old Wii Pro) controllers,
(which I mentioned on here in a prior post...) and I'm pretty happy with its performance.
Other people say they experience problems, but I don't get those... but then again, I also
just use Joy2Key and ignored the supplied software disc. The idea of using the Pro, which
is totally wireless, seems pretty cool though... but I'd have to hold one in my hands and be
able to judge the build quality before I'd even consider paying $50 for one to use on my PC.

The descrip on their site also says that it has a DirectInput mode, I'll go out on a limb
and assume that means that it can still function as a regular Windows HID device like
prior models for the old original Wii controllers.

Also yes, I realize that most "smart people" can already do this using Glovepie / PPJoy
and a BT dongle and a whole bunch of other stuff, but this adapter (and the adapter before
it for the original Classic Controllers) is mainly for us lazy, plug n' play types.